Control systems for offshore drilling and production well operations often require the use of both electrical and hydraulic control means. In prior proposed control systems, separate control lines carried electrical and hydraulic power to the sea floor for remote control well equipment located at the sea floor. Such separate control systems included separate, independently operable connect and disconnect means usually located at the sea floor installation.
In the event of severe ocean surface conditions such as caused by high winds and waves, it may be desirable to quickly disconnect control lines from the seabed installation to avoid and limit damage to equipment both at the sea floor and at the sea surface and to permit retrieval of control lines and riser portions. Where water depth is not great, the time for retrieval of control lines and riser portions is relatively short. In deep water, the retrieval time for control lines and riser portions may require a relatively long time, for example one or more days depending upon the depth of the water. In proposed deep water production riser systems, the riser may comprise an upper, relatively short riser portion and a lower, relatively long riser portion. The upper and lower riser portions may be connected by a buoyant structure located at a suitable depth as shown in copending U.S. application Ser. No. 771,799 filed Feb. 24, 1977 and owned by a common assignee. In such a proposed riser system, it is desirable to disconnect the upper riser portion at and slightly above such a buoyant structure to permit rapid retrieval of relatively short control lines and associated upper riser portion while the lower control lines and lower riser portion are supported by the buoyant structure in upright, free-standing position. Rapid disengagement of control lines from the vicinity of the buoyant structure is desirable so that the upper control line portions and associated riser may be retrieved and recovered before damage thereto may occur because of surface storm conditions. In such a proposed production riser, it will be understood that when a rapid, quick disconnect is made of control lines and riser portions that fail-safe valves operable below the point of disconnect will prevent pollution of the surrounding sea water.